The present invention relates to a liquid-crystal display having a dichroic polarizing layer that passes a light component of one polarization and absorbs a light component of another polarization, a polarization separation layer that passes a light component of one polarization and reflects a light component of another polarization, and a liquid-crystal cell, the retardation value or liquid crystal directors of which change in response to an electrical field.
A liquid-crystal display modulates polarized light obtained by passing the light through a polarizer and, as shown in FIG. 31, in a typical liquid-crystal display 1 of the past, light exiting from a light source 2 is caused to strike a light-absorbing type of dichroic linear polarizer 3, the linearly polarized light obtained therefrom being made to strike a liquid-crystal cell 4.
In the liquid-crystal display 1, light that strikes the liquid-crystal cell 4 and passes therethrough as polarized light, is modulated by the action of a voltage applied to electrodes provided on the liquid-crystal cell 4, which generates an electrical field that changes the liquid crystal within the cell is changed, or exits from the liquid-crystal cell 4 unchanged if there is no electrical field, after which, by the action of an absorption type dichroic linear polarizer disposed outside the liquid-crystal cell 4, light of only a specific polarization direction is transmitted.
The absorption type dichroic linear polarizers 3 and 5 pass polarized light of a transmission axis direction, and absorb almost all light of a direction perpendicular to the transmission axis direction. Therefore, approximately 50% of the light (unpolarized light) exiting from the liquid-crystal display 2 is absorbed by the dichroic linear polarizer 3, so that there is an overall decrease in the efficiency of light usage in the liquid-crystal display 1, and to achieve a sufficient intensity at the liquid-crystal display screen, it becomes necessary to cause a large amount of light from the light source to strike the dichroic linear polarizer 3.
However, if the amount of exiting light from the light source 2 increases in this manner, there is not only an increase in electrical power consumption, but also an increase in the heat generated by the light source 2, thus leading to the problem of an adverse affect on the liquid-crystal cell 4.
In contrast to the above, as disclosed in PC (WO) 4-502524 and the Japanese Unexamined Patent Application publication 6-130424, there has been a proposal of a liquid-crystal display in which, non-polarized light from a light source is separated into right-rotational or left-rotational circularly polarized light, by means of transmission or reflection using a cholesteric liquid-crystal layer, circularly polarized transmitted light of one rotational direction being caused to strike a liquid-crystal cell, and circularly polarized reflected light of another rotational direction being reflected, so as to reverse its rotational direction and cause it to pass through a cholesteric liquid-crystal layer, thereby improving the efficiency of light usage.
As disclosed in PC (WO) 9-506985, there has been a proposal of a liquid-crystal display in which non-polarized light from a light source is separated into two linearly polarized lights by transmission or reflection using an extended multilayer film, one transmitted linearly polarized light being caused to strike a liquid-crystal cell, and the other, reflected linearly polarized light having a direction that is perpendicular to the aforementioned light having its polarization direction changed, and being guided back to the extended multilayer film, thereby improving the efficiency of light usage.
In the liquid-crystal displays disclosed in the PC (WO) 4-502524 and the Japanese Unexamined Patent Application publication 6-130424, when no electrical field is applied to it, liquid-crystal layer shifts the phase of light an amount of either π(λ/2) or π/2 (λ/4), and when an electrical field is applied the liquid-crystal layer does not shift the phase of the light, light exiting from this liquid-crystal layer striking a circular polarizer disposed outside, it being transmitted or reflected, in accordance with its degree of polarization.
In the liquid-crystal display disclosed in PC (WO) 9-506985, linearly polarized light of one direction that has passed through an extended multilayer film is caused to strike a liquid-crystal cell, although there is no disclosure with regard to the retardation of the liquid-crystal layer.
In the liquid-crystal displays disclosed in PC (WO) 4-502524 and Japanese Unexamined Patent Application publication 6-130424, for the following reason, there is an extreme worsening of readability in the liquid-crystal display, and a great loss of contrast, making the display quality insufficient.
Specifically, in the liquid-crystal display of PC (WO) 4-502524, because a circular polarizer disposed outside of the liquid-crystal layer and directly visible is made from a low pitch cholesteric applied film having spectrally selective reflectivity, approximately 50% of the external light striking this circular polarizer is reflected, so that this directly entering the eyes of an observer, thereby causing a severe worsening of readability.
In the same manner, in the liquid-crystal display of Japanese Unexamined Patent Application publication 6-130424, the color-selective layer that is directly observable from the outside is a circular polarizer made of a cholesteric liquid crystal, and this, similar to the case cited above, directly reflects approximately 50% of the incident external light, thereby greatly reducing the readability of the display.